1. Technical Field
The invention relates to a piezoelectric actuator, a robot hand, and a robot.
2. Related Art
A piezoelectric actuator using resonance of a vibrating body including a piezoelectric device is driven with high efficiency by setting the frequency of a driving signal supplied to the piezoelectric device so as to approach the resonance frequency of the vibrating body. Since the resonance frequency of the vibrating body varies with changes in ambient temperature or load, there is disclosed a configuration of a piezoelectric actuator in which whenever activated, the frequency of a driving signal is changed and adjusted to the resonance frequency to thereby create a state where the piezoelectric actuator is driven with high efficiency quickly (for example, see JP-A-11-18449).
In the piezoelectric actuator disclosed in JP-A-11-18449, among the frequency of a driving signal, a longitudinal vibration driving voltage, and a flexural vibration driving voltage during low-speed driving, after only the frequency is changed, the flexural vibration driving voltage is increased to increase the rotating speed while maintaining the frequency and the longitudinal vibration driving voltage. In this way, a wide dynamic range from low-speed driving to high-speed driving is realized.
However, when the frequency of the driving signal is changed at the time of activation, the piezoelectric actuator passes through a frequency range where the piezoelectric actuator is not in a stable driving state. In such a frequency range, since it is difficult for the sliding portion of the piezoelectric actuator to follow a normal elliptical orbit, the reverse rotation, the abrasion of the distal end of the sliding portion, and the like may occur. In the worst case, the sliding portion may be destroyed. As a result, it becomes difficult to reliably activate the piezoelectric actuator in a stable state.